The main options are top-posting — in which the reply precedes the quoted original message; bottom-posting — in which the reply follows the quote; or interleaved posting - also called replying inline. While each online community differs on which styles are appropriate or acceptable, within any community the use of the "wrong" method risks being seen as a major breach of netiquette, and can provoke vehement response from community regulars.
For users of modern e-mail clients and "intelligent" e-mail services like Google mail, which display entire e-mail threads in logical order and hide extraneous content, the distinction between different posting styles is often now less relevant.
Top-posting includes the entire parent message (and usually previous messages) verbatim, with the reply above it. It is sometimes referred to by the term TOFU, an acronym for "Text Over, Fullquote Under". It is the default implemented by Microsoft Outlook, Outlook Express, Gmail, and others, and resembles forwarding messages with new text prepended at the top. Example:
The message is responded to with another full-length message, similar to traditional written correspondence except that the response includes the original message. While top-posting is sometimes recommended against, it is the more common style in business e-mail correspondence. Customer service e-mail practices often require that all points be addressed in a clear manner without quoting, while the original e-mail message may be included as an attachment merely as evidence.
One benefit of the style is that when a new correspondent is included in an otherwise private discussion (due to forwarding or addition of new recipients), the background of the discussion, or "thread", is also accessible, with the most recent response immediately visible at the top. Especially in business correspondence, an entire message thread may need to be forwarded to a third party for handling or discussion. In this case, it is appropriate to "top-post" the handling instructions or handoff discussion above the quoted trail of the entire discussion — as the intention is simply to "approve" or "provide instruction", not to respond in a point by point manner — or to send a copy of all the e-mails comprised by the discussion. (In environments where the entire discussion is public, like newsgroups or online forums, inclusion of past discussion is not necessary, and trim-posting is sufficient.)
E-mail has long supported a convention for forwarding verbatim an entire message, including its header. An untrimmed quoted message is a weaker form of transcript, as key pieces of meta information are destroyed. (This is why an ISP's Postmaster will typically insist on a forwarded copy of any problematic e-mail, rather than a quote.) These forwarded messages are displayed in the same way as top-posting in some mail clients.
The default quote format and cursor placement of many popular e-mail applications, such as Microsoft Outlook and Gmail, encourages top-posting. Microsoft has had a significant influence on top-posting by the ubiquity of its software; its e-mail and newsreader software places the cursor at the top by default, and in several cases makes it difficult not to top-post (this is caused by a bug present on most flavours of Microsoft Outlook where the quotation symbols are lost when replying in plain text to a message that was originally sent in HTML/RTF, along with the fact that on the default Microsoft Outlook setup, no quotation symbols are generated at all — this makes it very hard to distinguish between new and quoted text); many users have accepted this as a de facto standard. In addition, users of mobile devices, like BlackBerries, are encouraged to use top-posting, because the devices only download the beginning of a message for viewing. The rest of the message is only retrieved when needed, which takes additional download time. Putting the relevant content at the beginning of the message requires less bandwidth, less time, and less scrolling for the Blackberry user.
Partially because of Microsoft's influence, top-posting is more common on mailing lists and in personal e-mail. Top-posting is viewed as seriously destructive to mailing-list digests, where multiple levels of top-posting are difficult to skip. The worst case would be top-posting while including an entire digest as the original message.
Some believe that "top-posting" is appropriate for interpersonal e-mail, but inline posting should always be applied to threaded discussions such as newsgroups. Objections to top-posting on newsgroups, as a rule, seem to come from persons who first went online in the earlier days of Usenet, and in communities that date to Usenet's early days. Among the most vehement communities are those in the Usenet comp.lang hierarchy, especially comp.lang.c and comp.lang.c++. Top-posting is more tolerated on the alt hierarchy. Newer online participants, especially those with limited experience of Usenet, tend to be less sensitive to arguments about posting style. The classical reverse chronological post ordering used in weblogs is essentially top posting.
This example is occasionally used in mailing lists to mock and discourage top-posting:
Another style of replying to messages has been dubbed "bottom-posting". The reply is placed below the quote to preserve the logical order of the replies and follow the Western reading direction from top to bottom.
This is typically done when only a single portion of the previous message is being replied to; the rest of the quoted material is trimmed.
Scrolling down through a post to find a reply is inconvenient, especially for short replies to long messages, and many inexperienced computer users may not know that they need to scroll down to find a reply to their query. When sending an untrimmed bottom posted message, one might indicate inline replies with a notice at the top such as "I have replied below." However, as many modern mail programs are capable of displaying different levels of quotation with different colors (as seen here), this is not so much of an issue any more. Another good method to indicate that there is more reply text still to come is to always end your text with a signature line. Then the reader will know to continue to read until your signature line appears. This method is particularly polite and useful when using the inline reply method, since it tells the reader that your response is complete at the point where your signature line appears.
Inline replying style (or "interleaved reply", "point-by-point rebuttal", though it is sometimes also called "bottom-posting") was the original Usenet standard invented and used years before the existence of the WWW and the widespread public use of e-mail and the Internet in general. It is a format that can include "top-posting" for comments that need to precede one's response to specific points of what is being responded to. It can also include "bottom-posting" for introducing new material or summarizing what has been said in response to specific points of the text being replied to. However its major method and great advantage over previous hard copy correspondence methods is in giving a specific response to each paragraph, sentence or even phrase of the text of the message being replied to. This creates a natural, chronological ordering to each segment of the discussion stored within a message and helps make clear that the responder has read/understood all of the post being responded to. Since paraphrasing is not necessary, the ambiguities, omissions, misunderstandings or outright intentional distortions inherent in paraphrasing are avoided and comments are made point-for-point against the exact quote of the original message. Having response text aimed directly at what is being addressed makes for a more structured, disciplined and unambiguous reply. In addition the inline reply method enables and promotes much more forthright discourse by making it very clear where one's respondent has evaded, avoided, ignored, or simply missed responding to some point that was made. Some people think that proper netiquette for the inline reply method requires one to respond in some manner to all points that were addressed in a message of reply to one's original message, or else one is not being courteous and forthright. This is similar to an in-person conversation where when you ask a question to someone's face, you rightly expect a response, even if it is only to say "I don't want to answer the question". Only when one responds to a discussion in progress is it not impolite not to respond to all points of the person whose text one is responding to - ie. it is fully acceptable for a new responder to address only specific points of an ongoing discussion between others (again, just as if such a person had been listening to an in-person discussion and wanted to address only one specific point).
Inline replying is also frequent on Internet forums, and other situations in which the previous discussion is publicly available. However some webmail, most forum, and all blog commenting software do not have the inline possibility implemented in any easy way, usually because the previous message is not automatically quoted in the reply box and there are no prefixed level indicators. Inline was also originally used in all e-mail, but again with the advent of the WWW, vast numbers of new users, newly designed e-mail readers and webmail interfaces, most providers have abandoned the original standard, so that many users now do not even know of its existence, let alone its novel advances and advantages compared with older correspondence methods (which "top-posting" mimics).
Inline replies keep related sections of a discussion together within a message. As such it is easier to fork off parallel 'threads' of discussion from a single source message, each perhaps dealing with only one specific point (or subset of points) from the original.
As inline replying proceeds back and forth multiple indicators (left margin right angle brackets, or vertical bars, depending on the software and mode - text or html - that one is using) will build up (see examples below). These are called "levels" and their number indicates how many e-mails back is any text that is still within the ongoing discussion. If the discussion is between two people only, then, when in reply mode, the responder's text is always at the even levels (0,2,4,6, etc) and the text of the person being responded to is always at the odd levels (1,3,5,7, etc). However, when inline reply is being correctly used, since each new reply begins with an attribution line such as "Joe Blow wrote:", which text belongs to whom can always be determined by looking at the top of the post to see whose name is on the attribution line there which has one less of the number of level indicators than the text in which you are interested.
If quoting large sections of discussion, particularly in newsgroup discussions, it is recommended to trim the message such that only a taste of the original (a reminder) is left — even if this means leaving a sentence hanging. The chunks of quoted text are typically "trimmed" (leaving only the relevant quoted material), and some refer to this style as "trim-posting" or "edited-inline-posting". Paragraphs which are not replied to are frequently "snipped" completely. In such a circumstance it is customary to append an indicator, usually in the form of a square bracketed tag to the effect of [snipped], [trimmed], or simply [...]. However, note that good netiquette means that one does not snip material to which one has not made a response, otherwise it will not be clear to the receiver what parts of his text have been responded to and what not (or even read, for that matter). Therefore, snipping should only be done by a responder for text (including prior levels of that text) to which the sender has had no substantive comment and thus, with respect to which, discussion is essentially terminated. Snipping also prevents signature blocks, free e-mail service ads, and corporate disclaimers from piling up in a growing useless "tail" at the end of a post.
If the precise nature of the quote is not immediately apparent from the remaining text, it is polite to include a brief 'subject' text in the bracket, so the original author's words are not misunderstood by readers unfamiliar with the original. However, such paraphrasing of the previous text should never be used for a point-by-point reply, else misunderstandings, distortions and straw-man arguments can easily arise. Therefore, such paraphrasing of trimmed portions should not occur until any detailed discussion of the text therein is completed.
Many e-mail readers and web mail interfaces implement top-posting using the right angle bracket (">") prefix character (which indicates the level of the text in that line - number of previous replies in which it was written) and referred to as "prefix each line of the original" in Microsoft Outlook). This method is less popular with some people because lengthy reply histories can produce an awkward number of cascading prefix characters. However, good software reduces the spacing by placing additional prefix characters right next to each other and the use of methods of indicating reply levels by means of numbers of such prefix characters has some highly important advantages - see inline replying above for more information.
Another style called "double-quoting" involves replying in an interleaved manner to selected quotes from the original message, as described above, but then following this with a fullquote of the entire message, as if top-posting. This preserves the thread text in a single message, and also allows seeing what's being replied to in context. However this also results in some portions of the original message being quoted twice, which takes up extra space and might be considered confusing.
If you are sending a reply to a message or a posting be sure you summarize the original at the top of the message, or include just enough text of the original to give a context. This will make sure readers understand when they start to read your response.
This section of the RFC is discussing public archived postings such as mailing lists and newsgroups. For interpersonal e-mail, the subject line is often sufficient to remind the sender of what was being discussed, and no quoting of any type is necessary to indicate a reply. However, if one is politely addressing points of a conversation, the points discussed should be explicitly stated or quoted inline. This is stated in the RFC regarding interpersonal communication such as e-mail:
When replying to a message, include enough original material to be understood but no more. It is extremely bad form to simply reply to a message by including all the previous message: edit out all the irrelevant material.
Some would add that one should also include a blank line in between quoted material and responses to ensure that they are clearly set off from one another. Some mail programs may even try to re-word-wrap entire paragraphs and cause quotes and replies to be jumbled together illegibly if they are not cleanly separated. Newer e-mail software that operate in HTML e-mail mode, and use a left vertical bar instead of prefix right angle brackets (">"), attempt to enable word wrapping without spillover to lines with an incorrect number of level indicators, but are seldom successful unless both respondents are using the same software. A common mistake is to leave "tails" of right angle brackets (or left vertical bars) above or below a quoted block, running into the preceding or following paragraph of new material, instead of creating an entirely blank line as a separator.
Since quoted material frequently becomes several levels deep, if a relevant point is retained during a discussion, "attribution lines" are commonly used to indicate the author of each part of the quoted material. Because some people may think that the color of the examples below implies that the color of the attribution line means that such person wrote the text of that color (which is not true), it is important to realize that when color is used by software it is applied to all text of the responder, which includes the attribution line for the previous responder which is placed at the start of the message by the software when a reply is performed. Thus in the example below which is the current message as sent by Nancy and read by Alfred, it is Alfred that wrote the level 3 text "Do you like ..." and Nancy who replied with "No." (at level 2). After that, Alfred replied (at level 1) "How come?" and finally Nancy responded (at current level 0) with "I prefer to reply inline."
Many mail user agents will add these attribution lines automatically to the top of the quoted material. Retaining these lines as the discussion continues results in the following style. Note that the level indicator of the attribution line is always one less than the text of the attribution.